The present invention relates to a method of manufacturing an ultrasound transducer for use in an ultrasound imaging device. The present invention further relates to an ultrasound transducer manufactured according to the method. The present invention further relates to an ultrasound probe including at least one ultrasound transducer manufactured according to the method.
Ultrasound transducers are, for example, applied in ultrasound imaging devices. Herewith, images can be made of, for example, the heart of a human or animal. As the esophagus is close to the heart, often trans-esophageal echos (TEE) are made with such ultrasound transducers to visualize the heart. The TEE probes including the ultrasound transducers are arranged to generate images with a resolution corresponding to the aperture of the beam, the used frequency and the amount of transducer elements on the tip of the probe, among others. Other applications for such ultrasound transducers are also known, for example, to be applied in a blood vessel, heart chamber, or body cavity such as the vagina, rectum or nose to examine organs such as the uterus, prostate, stomach and so on.
Ultrasound imaging devices include, as described above, an ultrasound probe including the transducer having a plurality of individual transducer elements. Further, they include a central processing unit that controls the probe and renders the images from the acoustic signals derived from the probe. The central processing unit, in the form of a computer, can further be connected with a display to display the images, a keyboard or other input device to control the computer, and often storage devices to store the images thereon.
The probe forms an important part of the ultrasound imaging device, as it contains the transducer elements that transmit and receive ultrasound energy towards and from the target area, for example, the heart. Probes are found in different shapes and sizes, depending upon the application. Large probes can include a greater number of transducer elements and electronic circuitry, which has a positive effect on the resolution of the image. However, when larger probes are used internally, they are uncomfortable and allow less freedom of movement. With regard to the esophagus of a child, it is sometimes impossible to use a large probe at all.
It is known to arrange the transducer elements in a one dimensional array to generate a two dimensional image. One dimensional arrays can be steered, rotated or translated by the operator. These movements of the probe, however, can be very uncomfortable for the patient when used internally.
State of the art ultrasound transducers include a plurality of transducer elements arranged in a two dimensional array to generate a three dimensional image. Even four dimensional images are known, wherein plural images generated from a two dimensional array are combined over time, giving a real time, or near real time, three dimensional image.
Disadvantageously, two dimensional array ultrasound transducers are complex. They include, for example, a carrier layer having a two dimensional array of conductive pads and a plurality of piezo electric elements thereon. With the piezo electric elements, mechanical stress (vibration) is converted to and from an electrical potential. The piezo electric elements are on one side electrically connected with an individual conductive pad, and on the other side electrically connected with the other piezo elements and grounded, typically by applying a grounding layer over the plurality of individual piezo elements. As these transducer elements are arranged in a two dimensional array, the amount of transducer elements is very large, especially if a certain image resolution is required. For example, a relative small array of 32×32 includes 1,024 transducer elements. Each transducer element is connected individually, as the electrical signals transmitted or received therewith/therefrom are provided or read for further processing. Manufacturing these arrays is thus challenging.
Optimum transducer performance requires an optimum acoustic isolation of the array between each individual element. A gap between the elements filled with air may provide such an acoustic isolation. These gaps, however, increase the structural dimensions of the array and make the individual elements less stable as the physical strength of the array is lowered because of the gaps. The process of dicing the individual transducer elements from the array is also a delicate step in the manufacturing of the ultrasound transducer.
Furthermore, as each transducer element needs to be connected individually for applying an electrical signal or to read-out the electrical signal, connecting the transducer elements is challenging. Connecting each individual transducer element for further processing outside the probe would require a cable bundle with a huge amount of wires. This would not be practical because a cable with a large number of wired would be too large and inflexible to be provided through the esophagus or other body cavities. Therefore, at least some electric circuitry is needed in the probe to drive a group of individual transducer elements and lower the amount of wires needed. Electric circuits, however, increase the dimensions of the probe and complicate its construction.
Accordingly, there is a need for an ultrasound transducer that provides a high resolution image using an array of transducer elements, wherein the probe is smaller and less complex than conventional transducers.